CATALYTIC ENANTIOSELECTIVE HYDROSILYLATION OF AROMATIC KETONES USING RHODIUM COMPLEXES OF TADDOL-DERIVED CYCLIC PHOSPHONITES AND PHOSPHITES

Cyclic phosphonites and phosphites 24 are readily available from Cl2PR and (R,R)- or traaryl-1,3-dioxolane-4,5-dimethanols( = TADDOLs 1, which, in turn, are only two steps away from tartrate); the X-ray crystal structure of one representative, the phenyl phosphonite 2b, was determined. Five previously described and six new ones of the chiral P derivatives were tested as ligands for Rh(I)- and Pd0-catalyzed reactions such as hydrocarbonylations, hydroborations, and hydrosilylations of C=C bonds; while the resulting catalysts were highly active and regioselective, they did not lead to useful enantiomer enrichment in the products (Scheme 1). In contrast, hydrosilylation of phenyl and 2-naphthyl methyl or ethyl ketone by Ph2SiH2 (1.2 equiv.) gave, after desilylation, the corresponding secondary alcohols of (R)-configuration with up to 87 % ee in the presence of 0.1 equiv. of the penta(2-naphthyl)-substituted phosphonite 3d and 0.02 mol-equiv. of Rh (Table 1).